The present invention relates in general to optical data transmission and, more particularly, to optimizing electronic data waveforms for optical transmission prior to their conversion to optical signals.
It is known in the art that in transmitting high speed optical signals, both laser devices and light emitting diodes are not balanced in their "turn-on" and "turn-off" characteristics. Consequently, a signal transmitted over a fiber optic medium is unbalanced in that the resultant duty cycle will be more or less than 50 percent. Electronic circuits implemented in integrated circuit semiconductor technologies, such as bipolar emitter-coupled logic and gallium arsenide MOS, have demonstrated capabilities for operating at frequency ranges of 600 megahertz to several gigahertz. Coupling these high performance circuits to drive optical devices, that in turn drive fiber optic cables, results in less than ideal optic system performance due to the unbalanced duty cycle presented to the optical medium. Therefore, the advantages of using a high frequency semiconductor technology front-end is negated at the back-end fiber optic interface.
In the past, attempts to remedy this problem have included the addition of compensating resistor/capacitor networks to the outputs of the circuits that drive the optical devices. These networks are custom designed for a specific system operating frequency and for the operating characteristic of the light emitting source. As a result, the range of applications is very narrowly limited, and the same circuit must be redesigned for varying transmitting devices and mediums.
Hence, a need exists for a universal apparatus and method for producing variable electronic driving signals for optical devices that compensate for the mis-match in "turn-on" and "turn-off" characteristics of the optical devices and thus provide an optimized transmitted optical signal.